Although still controversial, increasing evidence suggests that intrinsic beta cell defects are responsible for human diabetes mellitus. The observation that both circulating insulin levels and the number of beta cells are significantly reduced in diabetes calls attention to the need for gaining increased insight into the natural history of the beta cell, and for delineating the mechanisms which control beta cell neogenesis, and insulin biosynthesis, storage and release. The objectives of this study are: 1. to delineate the factors which regulate beta cell neogenesis; 2. to elucidate the genetic mechanisms which control insulin synthesis; and 3. to explore the feasibility of utilizing implantation of beta cells maintained in tissue culture as a means for treating diabetics. Tissue culture techniques will be used both for implantation studies and to examine beta cells from various species including rodents and primates under controlled in vitro conditions for extended periods of time. The recent development of a transplantable rat insulinoma with high insulin content has facilitated a number of studies in which limitation of starting material posed a major obstacle. These insulinomas can be employed as a source of beta cells for tissue culture, for isolation of beta cell plasma membranes and other subcellular organelles, and for isolation of messenger RNA for insulin synthesis. Islet cell morphology and beta cell replication will be examined by light and electron microscopy and by radioautography. Insulin biosynthesis will be studied using labeled amino acid precursors and column chromatography and insulin secretion using the double antibody immunoassay technique. Messenger RNA for insulin will be examined using cell-free translation systems, and purified messenger employed as a template for synthesis of the insulin gene. BIBLIOGRAPHIC REFERENCES: King, D.L. and Chick, W.L.: Pancreatic beta cell replication: Effects of hexose sugars. Endocrinology 99: 1003-1009, 1976. Duguid, J.R., Steiner, D.F. and Chick, W.L.: Partial purification and characterization of the mRNA for rat preproinsulin. Proc. Natl. Acad. Sci., USA 73: 3539-3543, 1976.